<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>点击鼠标</title>
    <style>
        .bigbox{
            width: 100px;
            height: 100px;
            border: 1px solid black;
        }
    </style>
</head>
<body>
    <div class="bigbox">
        <th>
            <tr style="border: 1px solid black;">
                <td></td>
            </tr>
        </th>
    </div>
    <script>
        const tr = document.querySelector('tr');
        for(let i =0;i<tr.length;i++){
            
        }
    </script>
</body>
</html>